Installing an SSL cert for NodeJs express (for API) on my Windows server

Question

all my servers are hosted locally. I use IIS on server 2019 to host and manage my website. I use NodeJs to act as an API which makes queries to my SQL server to get the information and return it to my React app.

my react app calls out to my NodeJs API using fetch url

var url = 'https://example.com:8080/api/locationInfo/client?client=%';
    fetch(url, {agent})
        .then(response => response.json())
        .then(data => setLocationInfoData(data));

since my website is using HTTPS, i must use that in the URL that reaches out to the API service from NodeJs.

right now when i attempt to make these API calls, console is giving me the error: net::ERR_SSL_PROTOCOL_ERROR

im assuming this is because my NodeJs app does not have an SSL certificate installed.

I've spent many (many) hours of research, but im not experienced with the backend of web development and im having trouble understanding where and how i apply an SSL cert to my NodeJs API. I used IIS to create a self-signed certificate, but it hasnt been applied anywhere and nothing else was done; im not sure where to go from here.

if it matters, my NodeJS API is hosted on the C:\Program Files[...] directory of the server, not under the actual web hosted directories.

If i place the NodeJs app within the actual web hosted directories, would i still need a certificate? If so, how do i export the .key and the .crt files to include in my NodeJs code?

please let me know if i can provide any more information or any of my code. My experience is limited, but im determined to learn and just need some pointers to send me in the right direction.

EDIT: i created a PFX cert from windows and used openSSH to convert the key, ca, and cert to .pem and included those in my nodeJs application. now im getting "ERR_SSL_KEY_USAGE_INCOMPATIBLE"

nodeJS code:

const sslServer = https.createServer(
{
   key: fs.readFileSync(path.join(__dirname, 'cert', 'key.pem')),
    cert: fs.readFileSync(path.join(__dirname, 'cert', 'cert.pem')),
    ca: fs.readFileSync(path.join(__dirname, 'cert', 'ca.pem')),   
  },    
app

)